1. Field of the Invention
The present invention relates to a process for removing a silicon-containing film for lithography used for fine processing in a manufacturing process of semiconductor devices and the like.
2. Description of the Related Art
With highly integrated LSI's providing highly increased speeds, finer pattern rules are being rapidly promoted. Commensurately with the fineness, the lithography technique has attained formation of fine patterns, by virtue of light sources of shorter wavelengths and resist compositions appropriately selected therefor. The main role thereof was played by positive photoresist compositions to be each used as a monolayer. The monolayer positive photoresist composition is configured to possess, in a resist resin, a frame having an etching resistance against dry etching by chlorine-based or fluorine-based gas plasma, and to possess such a resist mechanism that an exposed portion is made dissolvable, so that the exposed portion is dissolved to thereby form a pattern, and the remaining resist pattern is used as an etching mask to dry etch a processing substrate coated with the resist composition.
However, when a pattern is made finer, i.e., pattern rules are further narrowed while keeping a thickness of a used photoresist film as it is, the photoresist film is deteriorated in resolution performance. Further, when the resist film is to be developed by a developer to form a pattern, a so-called aspect ratio thereof is made excessively large, thereby resultingly causing a pattern collapse. Thus, the fineness has been accompanied by decrease in photoresist film thickness.
Meanwhile, although for processing of a processing substrate, there is typically used a method for processing the substrate by dry etching by adopting a patterned photoresist film as an etching mask, practically no dry etching methods exist to exhibit a complete etching selectivity between a photoresist film and a processing substrate, so that the resist film is also damaged during processing of the processing substrate and the resist film is collapsed, thereby failing to accurately transfer a resist pattern onto the processing substrate. Thus, with finer patterns, resist compositions have been required to have higher dry etching resistances.
Further, since shortened wavelengths of exposure have demanded that resins having lower light absorption at exposure wavelengths are used for resist compositions, such resins have been subjected to a transitional history from a novolak resin, through polyhydroxystyrene, and to a resin having an aliphatic polycyclic frame, commensurately with a transitional history from i-beam, through KrF, and to ArF. However, etching speeds under the dry etching condition have been practically made higher, so that recent photoresist compositions having higher resolutions practically tend to be rather lowered in etching resistance.
This obliges a processing substrate to be dry etched by a photoresist film which is inevitably thinner and weaker in etching resistance, thereby making it urgent to ensure a material and a process in this processing state.
As one method to solve such a problem, multi-layer resist process have been used. The multi-layer resist process further include a three-layer resist process which can be performed by using a typical resist composition used in a monolayered resist process. For example, this method is configured to form: an organic film as a resist under layer film based on novolak or the like on a processing substrate; a silicon-containing film as a resist intermediate film, thereon; and a typical organic photoresist film as a resist upper layer film, thereon. Since the organic resist upper layer film exhibits an excellent etching selectivity ratio relative to the silicon-containing resist intermediate film for dry etching by fluorine-based gas plasma, the resist pattern is transferred to the silicon-containing resist intermediate film by means of dry etching based on fluorine-based gas plasma. According to this method, patterns of novolak films having sufficient dry etching resistances for processing can be obtained insofar as patterns can be transferred to silicon-containing films, even by adopting: a resist composition which is difficult to be formed with a pattern having a sufficient film thickness for direct processing of a processing substrate; and a resist composition having an insufficient dry etching resistance for processing of a substrate.
Examples of silicon-containing resist intermediate films to be used in the above-described three-layer resist process include; as for films obtained by spin coating, such as SOG (spin-on-glass) films (Japanese Patent Laid-Open (kokai) No. H5-291208, J. Appl. Polym. Sci., Vol. 88, 636-640 (2003), for example), and crosslinkable silsesquioxane films (Japanese translation of PCT international application No. 2005-520354, for example).
Upon usage of such films in a process for manufacturing actual semiconductor devices, defects are occasionally caused in coated films formed on wafers, thereby inevitably requiring re-processing. To strip off silicon-containing films upon such re-processing, stripping has been conventionally conducted by a method such as dry stripping based on fluorine gas, which brings about considerable damages to wafers.
Meanwhile, sulphate ion-containing stripping solutions and fluoride ion-containing stripping solutions are known as stripping solutions, which are typically used in semiconductor production processes.
Although treatment of a silicon-containing film by such a typically used sulphate ion-containing stripping solution allows the sulfuric acid to remove organic substitutional groups and organic components contained in the silicon-containing film, siloxane bonds acting as main frames of the silicon-containing film are rarely decomposed then, thereby problematically failing to complete stripping of the silicon-containing film. In turn, although treatment of a silicon-containing film by a fluoride ion-containing stripping solution allows for cleavage of siloxane bonds, this treatment requires such a condition to avoid damages of a circuit having been formed on a silicon wafer, thereby obliging to use an extremely dilute stripping solution in a normal case. This certainly enables to break siloxane bonds at portions substantially close to a surface of the silicon-containing film, while leaving a problem that a complete stripping is unachievable.